SERVER-29462 Align locks in mongo::Paritioned to avoid false sharing

1 files changed, 65 insertions, 0 deletions

diff --git a/src/mongo/util/with_alignment.h b/src/mongo/util/with_alignment.h
new file mode 100644
index 00000000000..b1128f527ff
--- /dev/null
+++ b/src/mongo/util/with_alignment.h
@@ -0,0 +1,65 @@
+/**
+ * Copyright (C) 2017 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this exception statement from all source files in the program,
+ * then also delete it in the license file.
+ */
+
+#pragma once
+
+#include <algorithm>
+
+#include "mongo/stdx/new.h"
+
+namespace mongo {
+
+/**
+ * Creates a new type with the same interface as T, but having the
+ * given alignment. Note that if the given alignment is less than
+ * alignof(T), the program is ill-formed. To ensure that your program
+ * is well formed, see WithAligmentAtLeast, which will not reduce
+ * alignment below the natural alignment of T.
+ */
+template <typename T, size_t alignment>
+struct alignas(alignment) WithAlignment : T {
+    using T::T;
+};
+
+/**
+ * Creates a new type with the same interface as T, but having an
+ * alignment greater than or equal to the given alignment. To ensure
+ * that the program remains well formed, the alignment will not be
+ * reduced below the natural alignment for T.
+ */
+template <typename T, size_t alignment>
+using WithAlignmentAtLeast = WithAlignment<T, std::max(alignof(T), alignment)>;
+
+/**
+ * Creates a new type with the same interface as T but guaranteed to
+ * be aligned to at least the size of a cache line.
+ */
+template <typename T>
+using CacheAligned = WithAlignmentAtLeast<T, stdx::hardware_destructive_interference_size>;
+
+}  // namespace mongo